Core-a-te, an exercise class combining karate, self-defense, and core strengthening being taught by Whitney Arnautou at United Studios of Self Defense in San Francisco, Calif., on Monday, August 30, 2010.

Photo: Liz Hafalia, The Chronicle

Core-a-te, an exercise class combining karate, self-defense, and...

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Phyllis Swindells (front) from San Francisco winding down after doing Core-a-te, an exercise class combining karate, self-defense, and core strengthening in San Francisco, Calif., on Monday, August 30, 2010. P

Photo: Liz Hafalia, The Chronicle

Phyllis Swindells (front) from San Francisco winding down after...

Image 3 of 4

Pam Baer (front) from San Francisco participating in Core-a-te, an exercise class combining karate, self-defense, and core strengthening in San Francisco, Calif., on Monday, August 30, 2010.

Photo: Liz Hafalia, The Chronicle

Pam Baer (front) from San Francisco participating in Core-a-te, an...

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Tori Ritchie from San Francisco stretching in Core-a-te, an exercise class combining karate, self-defense, and core strengthening at United Studios of Self Defense in San Francisco, Calif., on Monday, August 30, 2010.

Arnautou first offered the class in March, after noticing many of her beginner martial arts students were getting winded. They could get into their forms and spar, but had no endurance.

She searched for a class that combined isometric core conditioning for martial artists but found nothing. So she secured the Core-a-te domain name and started teaching it herself. She added a second class to meet demand in September.

"I feel like if I don't do this class, I am setting myself up for back problems," said tennis player Julie Feldstein, 51.

"Your core is vital for any sport, but, as athletes, you can neglect it when you train in the same movements over and over."

Students who work their core for an hour twice a week can begin to see results in about a month, Arnautou said.

Julie Whitcomb, 51, feels stronger after six months of Core-a-te, but the biggest change is in her attitude toward exercising.

"I love starting the week this way, incorporating the balance drills, meditation and movements," she said. "This is a welcome place; there's no intimidating gym feeling."

In a recent class, Arnautou turned the stereo to Taio Cruz's "Break Your Heart," and led students through a series of kicks while holding her wrists in a protective boxer's stance.

Next students balanced on one foot.

"Now shut your eyes," Arnautou said. "See how much harder it is when you remove one of your senses."

After an hour of crunches, planks, leg lifts and power punches, it was time to retire to the backyard koi pond for some green tea.

The eight women gathered in the garden for another half hour, telling stories.

It was the right balance of socializing and exercising that Arnautou found lacking in the gyms where she used to work.

"Core-a-te is all about learning and growing at one's own pace," she said. "I feel that balance is imperative to this whole process of aging gracefully."